The science of humour: Why we laugh

Human beings love to laugh so much – on average 17 times a day for adults - that entire industries are built around laughter. Situation comedies, cartoons and stand up comics are all meant to make us chuckle and feel good about ourselves.

While it seems so natural to us, the funny thing about laughter is that it is actually a very complicated and unique mental and physical response.

First of all, laughter is not the same thing as humour. To put it dryly, laughter is the physical consequence of humour. At its bare minimum a laugh has two parts: a facial gesture and an audible sound. However, when we guffaw with gusto many more bits of the body join in - knees get slapped and muscles in the midsection contract for that belly shaking sensation.

Ever laughed so hard you cried? That happened because your epiglottis - the little flap at the back of your throat – closed down a bit, restricting your air intake. Meanwhile your tear ducts kicked in with each gasp for breath and your face probably turned quite red.

Like coughing and sneezing, laughter is an involuntary, automatic response by the body. However, there is a difference between them. Sneezing is caused by direct stimulation of the nervous system. Take a whiff of pepper and see for yourself.

Laughing, on the other hand, results from indirect stimulation of the nervous system. Basically your brain needs to process the joke first and if the joke tickles your mind then your mind sets your nervous system to work.

Jokes, even your basic “knock-knocks,” are sophisticated verbal flourishes, the product of culture, intellect and linguistic skill impossible to reproduce under laboratory conditions. Outside of our closest relatives, the apes, no other animal does it.

While telling a joke is complex, higher-order communication, the way we enjoy the joke is totally primitive. Laughter – an involuntary, animal noise coupled with a physical response halfway between fear and ecstasy - flies below our intellectual radar, at the level of instinct.

While no one is completely certain why humans developed the ability to laugh in the first place, the most accepted theory is that it evolved as a response to threat or warning, or as a way of relieving tension when threat had passed. Since the relaxation that comes after a good chuckle inhibits our instinctual fight-or-flight response, laughter indicates trust in the company we keep.

People use humour to relieve stressful situations all the time. Perhaps the capacity to see the sunny side was an advantage when coping with the ordeals of early human hunting and gathering.

Many say laughter is contagious. If you don’t believe them, just look at what happened in Kashasha, a small village near Lake Victoria. On January 30, 1962, three girls at a missionary school began to giggle uncontrollably. Their classmates joined in and just couldn’t stop. The school was closed in March, but not before riotous laughter infected the entire area.

Eventually the whole town was quarantined and at the peak of the epidemic 1,000 villagers were affected. The area was not declared “laughter-free” until June 1964.